Magnetism and Matter 3 Flashcards
what are paramagnetic substances
Paramagnetic substances are those which get weakly magnetised when
placed in an external magnetic field. They have tendency to move from a
region of weak magnetic field to strong magnetic field, i.e., they get weakly
attracted to a magnet.
They develop feeble magnetisation in the direction of the magnetising field.
what is the origin of paramagnetism
Electrons in a paramagnetic material are randomly oriented. They have some net permanent magnetic moment.
In the absence of external field, the atomic dipoles are randomy oriented due to random motion. So no net magnetisation is produced
When a strong external magnetising field is applied, the atomic dipoles align themselved in the direction of the applied magnetic field, producing a weak dipole moment in the direction of the field.
The individual atoms (or ions or molecules) of a paramagnetic material
possess a permanent magnetic dipole moment of their own. On account
of the ceaseless random thermal motion of the atoms, no net magnetisation
is seen. In the presence of an external field B0
, which is strong enough,
and at low temperatures, the individual atomic dipole moment can be
made to align and point in the same direction as B0
what will happen when a paramagnetic substance is kept in an magnetic field.
The field lines
gets concentrated inside the material, and the field inside is enhanced. In
most cases, this enhancement is slight, being one part in 105
. When placed
in a non-uniform magnetic field, the bar will tend to move from weak field
to strong.
example of paramagnetic materials
Some paramagnetic materials are aluminium, sodium, calcium,
oxygen (at STP) and copper chloride
effecr of temperature of paramagnetic materials
- inversely proportional to temperature.
As the field is increased or the temperature is
lowered, the magnetisation increases until it reaches the saturation value
at which point all the dipoles are perfectly aligned with the field.
what are ferromagnetic materials
Ferromagnetic substances are those which gets strongly magnetised when
placed in an external magnetic field. They have strong tendency to move
from a region of weak magnetic field to strong magnetic field, i.e., they get
strongly attracted to a magnet.
they develop strong magnetisation in the direction of magnetising field.
origin of ferromagnetism
The individual atoms (or ions or molecules) in a ferromagnetic material
possess a dipole moment as in a paramagnetic material. However, they
interact with one another in such a way that they spontaneously align
themselves in a common direction over a macroscopic volume called
domain.
Each domain has a net magnetisation, in the absence of field. The direction of magnetic field of each domain is different as they are oriented randomly. At any instant, the net dipole moment is 0.
But in the application of a suitable magnetic field, all the domains are aligned in the same direction and hence a strong dipole moment is produced.
what happens when a ferromagnet is placed in an external field
Thus, in a ferromagnetic material the field lines are highly
concentrated. In non-uniform magnetic field, the sample tends to move
towards the region of high field.
what are
i) hard magnets
ii) soft magnets
In some ferromagnetic materials the
magnetisation persists, even after removal an external magnetising field. Such materials are called hard magnetic materials
or hard ferromagnets. Alnico, an alloy of iron, aluminium, nickel, cobalt
and copper, is one such material. The naturally occurring lodestone is
another. Such materials form permanent magnets to be used among other
things as a compass needle.
On the other hand, there is a class of
ferromagnetic materials in which the magnetisation disappears on removal
of the external field. Soft iron is one such material. Appropriately enough,
such materials are called soft ferromagnetic materials.
example of ferromagnet
There are a number
of elements, which are ferromagnetic: iron, cobalt, nickel, gadolinium,
etc. The relative magnetic permeability is >1000!
what is the relation between ferromagnetic’s susceptibility and temperature.
The ferromagnetic property depends on temperature. At high enough
temperature, a ferromagnet becomes a paramagnet. The domain structure
disintegrates with temperature. This disappearance of magnetisation with
temperature is gradual.
what is curie’s law
Susceptibility of a paramagnetic substance is inversely proportional to absolute temperature.
x ∝ 1/T
x =C/T
C- curies constant
what is curie weiss law
it statses that the susceptibility of the ferromagnetic material above curie temperature is inversely proportional to the excess of temperature above curie temperature
x ∝ 1/T-Tc
x ∝=C/T-Tc
what is curie’s temperature
As the temperature increases, the magnetisation of ferromagnetic substance decreases. At a particular temperature, it becomes paramagnetic. Taht temperature is called curie temperature. it is diff for diff materials.
